Derailment of a railroad tank car often causes loss of the contents of the car when the bottom outlet valve of the car is knocked off or severely damaged. It has not been possible to adequately protect a bottom outlet valve with a simple skid arrangement when the valve discharges through a tee that permits unloading from either side of the car. The arms of the tee are large surfaces exposed to the danger of impact, and these arms also function as levers increasing the forces that damage or shear off the valve. Also, malfunctioning of prior art safety devices can be caused by impact that occurs after such devices are triggered.